Door openers for garage doors are known which are operated by radio-control units and serve to raise and lower a garage door. Such devices normally have a motor that is provided with a sprocket over which a chain connected to the door is spanned. A radio-control receiver is connected to this motor is operate it in a direction tending to close the door if it is in the open position or to open the door if it is in the closed position each time it receives a signal from a transmitter normally carried in the vehicle that uses the garage.
Such units are typically relatively bulky. They normally use a motor having a capacity of at least one-fifth horsepower, and normally weigh at least 20 kilograms. It is necessary to provide such a large motor as stepping down the force of a smaller motor can result in serious accidents should the door strike a person or vehicle while opening or closing. A larger motor can stall without being seriously damaged while a smaller motor that is stepped down to derive the same torque would be damaged.